I've got a Jacobs Exhaust brake that was given to me by a friend. It has a brand new solenoid and wiring harness. The only used part of the brake is the butterfly/diaphram assembly.

Here's the problem. The brake "hangs" shut when I'm taking off from a dead stop. On the interstate and at highway speed, it works like a champ.

The way that it works (for those that may be unfamilliar) is that there is a wire going to the ECM (computer) that energizes the solenoid when it sees ZERO throttle. There's a couple second delay before it engages (in case you are shifting gears and not braking). When I hit the throttle while moving down the road, it releases instantly. However when I leave from a stop, it takes about 7 seconds for the brake to release... as you might imagine, it really holds the truck back. Not to mention the smoke that this creates.

For troubleshooting, I've taken the brake off, and cleaned it really good. I've also sanded down the edges a little.

It seems to me that what's happening is that the vaccum pulls it shut, and then it gets stuck on soot buildup or something. When the drive pressures are higher (like at highway speed), there's enough pressure to break it loose... when leaving from a stop, it takes a little while to build up enough pressure to knock it loose. That's my theory anyway. Someone shoot it down if it doesn't make sense.

Any other ideas? More aggressive sanding/grinding with a dremel or something?

 

I have the same exact brake on my truck with 110k miles on it and have had zero problems with it..................here is my take on this

the actuator for this brake is a fail open system meaning that if you loose vacumn to it then it will fail open so if you dont have the switch flipped then it should be in the open position as long as there is zero fuel being added..........this is detected by pin #20 (I think) of the ecm...........with that being said you still may have issues with the actuator hanging up the valve in the closed positin..........I would lube up the actuator good with some pennitrating oil to make sure.

the other thing is like you say and the butterfly valve may be hanging up on the body.................check it out real good when the actuator is off the body .

the only other thing that I can think of is maybe the body of the valve is in a bind causing distortion and a hangup......this is highly possible if you have big pipe stress on the system

Cheers,Kevin

 

Thanks Kevin. before I take the whole assembly off the turbo again, I think I'm going to wire a small LED off the pin in the ECM. I should be able to wire it so that when the ECM energizes that circuit, the led will light. That way I can tell if the ECM is sending +12v to the solenoid from a dead stop.

I feel confident that the brake assembly is as clean and lubricated as it can be. Maybe it's not and I'll need to work with it longer.

I also cleaned that brass sintered filter that's on the solenoid. Jacobs and several people have mentioned that it could be a problem.

Thanks for the input... I'll keep fiddling with it.

 

what finally fixed this problem? mine does the EXACT same thing. thanks

 

never heard back from him but I am thinkin vacuum problems to the solonoid

 

Yup filter is one problem and then if that doesn't work, since they have a pretty strong return spring try removing the vacuum hose and see if it releases. If so, the vacuum solenoid is probably shot.

 

I finally gave up on it. Tried everything mentioned above more than once. The vac solenoid is brand new. Bought a new filter which didn't help.Tried hi temp lube... can't remember what else I did.

I finally just gave up on it. It's installed, but I rarely use it.

Works good to help warm up the truck, but that's about it.

 

what a trip. i just pulled the solenoid apart today and polished every part in it. the thing works perfect sitting in the driveway. just barely have to touch the juice pedal and it releases. take off and get stopped by a traffic light for more than a few minutes and it hangs up. it used to work perfect then just started screwing up. do you know if it's an actual switch that tells the ECM the pedal is off idle or part of the apps circuit? thanks

 

to andyman or anyone else with this problem this should fix it. inside the socket on the linkage there is a groove with a keeper wire in it. this little wire came out of the groove and got all twisted up in the socket. i pulled the pieces out and polished the chewed up part of the socket with a round stone on a die grinder. put the linkage back together using only the safety clip and now it works just like new. been trying to figure this out for a long time but because of the grease in the socket i couldn't see the stupid little wire. hope this helps someone else.

 

Cool! I hope this works for everyone else!